This is a case-control epidemiological study designed to ascertain whether there are any associations, either positive or negative, between use of exogenous estrogenic hormones for therapy during or following menopause or for oral contraception during reproductive years, and cancer of the corpus uteri, cancer of the breast, and cancer of the ovary. Previous estrogen use in women in the age group 45 to 74 years admitted to several large Connecticut hospitals with a first diagnosis of any of these cancers will be compared to estrogen use in women of the same age group admitted to surgical services in the same hospitals for other conditions. Information on estrogen use and other relevant variables is obtained by means of a standardized structured questionnaire administered by trained interviewers; this is supplemented by information provided by the patient's physician when necessary. Diagnosis of the cancers is confirmed by a pathologist, and particular attention is focused on specific histologic types. The study is now in its second year of data collection. To date, 236 cases of breast cancer, 127 cases of endometrial cancer, 54 cases of ovarian cancer, and 1121 controls have been interviewed and the information keypunched and checked for errors. It is expected that data collection will be complete for breast cancer and endometrial cancer by June, 1979.